In imaging devices, such as digital cameras, it is typical to mount a filter unit on a lens barrel with the object of using the filter unit as a protector that protects the front surface of the lens from dirt and scratches or to, for example, polarize or reduce the light. A conventional filter unit, for example, is configured by fixing a discoidal glass filter body inside an annular filter frame body. Note that the annular filter frame body is configured such that a male screw portion for attaching a lens barrel is formed on one end side, and a female screw portion for attaching another lens related component is formed on the other end side.
In many cases, the filter frame body is attached to the filter body by, as proposed in PTL 1 described below, performing fixing with a presser ring or a C-ring after directly dropping the filter body in an inner surface of the filter frame. Furthermore, as proposed in PTL 2, in some cases, fixing is performed by caulking. In other words, the filter unit is made while the filter frame body and the filter body are in pressure contact with each other. Moreover, an example in which the filter frame is configured of polymeric elastomer is proposed in PTL 3. Since fixing is performed by a method such as thermal caulking, ultrasonic bonding, adhesion, or the like, it is considered that the filter frame body and the filter body are in a state of pressure contact with each other.
In recent years, in the technical field related to digital cameras, application of solid-state image sensing devices with a high-resolution performance such as 4K (horizontal resolution 4096 pixels×vertical resolution 2160 pixels), and further 8K (horizontal resolution 7680 pixels×vertical resolution 4320 pixels) are being considered. However, as in the filter units proposed in PTLs 1 to 3, when the filter unit is configured in a state in which the filter frame body and the filter body are in pressure contact with each other, there is a concern of a distortion occurring on the surface of the filter body. In such a case, if a 4K or an 8K solid-state image sensing device is used, there is a concern of deterioration in image caused by distortion in the surface of the filter.
In the invention described in PTL 4 described below, a technique is proposed that attempts to fix the lens to the barrel with an elastic adhesive. In the invention described in PTL 5 described below, a technique is proposed that prevents a center deviation from occurring after a light source and a light source holder are attached to each other by fixing the light source holder constituting a light source unit and an auxiliary member that is integral with a light source to each other with an elastic adhesive. As described above, in PTLs 4 and 5, inventions have been proposed that focus on relieving the distortion that occurs by contact between different members. Other than the above, a filter unit that is disclosed in PTL 6 has been proposed.